The Australian Big Bash League (BBL) continues to be in the grip of Covid-19 scare after Sydney Thunder's 29-year-old wicketkeeper-batter Sam Whiteman was ruled out of Sunday's game against Brisbane Heat at The Gabba as a precautionary measure while the club investigates whether he was a potential close contact with someone who had tested positive for COVID.The opener was replaced by 21-year-old Lachlan Hearne in the squad. Brisbane Heat won the toss and elected to bowl, with Sydney Thunder notching up 81/1 in 10 overs of the 20-over innings.A statement issued by Sydney Thunder on Sunday said that, "Upon learning yesterday (Saturday) of the possibility of his being a COVID-19 contact, Whiteman immediately reported his situation to Thunder's team management who followed COVID protocols."Whiteman has returned two negative COVID tests since becoming aware of the situation. The Sydney Thunder and Sydney Sixers players and support staff are all undertaking daily rapid testing during the BBL.Whiteman, who is in NSW, has been quarantined from Thunder's players, coaching, and support staff until further notice.With COVID-19 wreaking havoc, five BBL matches, including Perth Scorchers versus Hobart Hurricanes scheduled to be played at Optus Stadium, Perth on December 20, will have to be relocated to alternate venues after a Perth Glory player tested positive for the virus, Cricket Australia (CA) had said on December 16.